Left, an image of comet Chury showing outgassing of water vapor, which entrains dust. Right, the neck region, between the comet's two lobes. Various types of relief can be seen, including the dunes, at bottom left (circled in red), in the sandy region. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA)Surprising images from the Rosetta spacecraft show the presence of dune-like patterns on the surface of comet Chury. Researchers at the Laboratoire de Physique et Mécanique des Milieux Hétérogènes (CNRS/ESPCI Paris/UPMC/Université Paris Diderot) studied the available images and modeled the outgassing of vapor to try to explain the phenomenon. They show that the strong pressure difference between the sunlit side of the comet and that in shadow generates winds able to transport grains and form dunes. Their work is published on 21 February 2017 in the journal PNAS.

The formation of sedimentary dunes requires the presence of grains and of winds that are strong enough to transport them along the ground. However, comets do not have a dense, permanent atmosphere as on Earth. Nonetheless, the OSIRIS camera on board the Rosetta spacecraft showed the presence of dune-like forms approximately ten meters apart on 67P/Churyumov-Gerasimenko. They are found on the lobes of the comet as well as on the neck that connects them. Comparison of two images of the same spot taken 16 months apart provides evidence that the dunes moved and are therefore active.Faced with this unexpected finding, the researchers show that there is in fact a wind blowing along the comet's surface. It is caused by the pressure difference between the sunlit side, where the surface ice can sublimate due to the energy provided by the sunlight, and the night side. This transient atmosphere is still extremely tenuous, with a maximum pressure at perihelion, when the comet is closest to the Sun, 100 000 times lower than on Earth. However, gravity on the comet is also very weak, and an analysis of the forces exerted on the grains at the comet's surface shows that these thermal winds can transport centimeter-scale grains, whose presence has been confirmed by images of the ground. The conditions required to allow the formation of dunes, namely winds able to transport the grains along the ground, are thus met on Chury's surface.This work represents a step forward in understanding the various processes at work on cometary surfaces. It also shows that the Rosetta mission still has many surprises and discoveries in store.Explore further:Image: Rosetta's shadow crosses Comet 67P/Churyumov–Gerasimenko in daring encounterMore information: Pan Jia et al. Giant ripples on comet 67P/Churyumov–Gerasimenko sculpted by sunset thermal wind, Proceedings of the National Academy of Sciences (2017). DOI: 10.1073/pnas.1612176114Journal reference:Proceedings of the National Academy of SciencesProvided by:CNRS

*I've been reliably informed that not all volcanoes are conical. In fact it is only cinder cone volcanoes that have this shape. Shield, Dome and Composite volcanoes have different shapes to reflect the different processes of how they are formed.

It's a similar shape to piles of sand, piles of grain, and sand dunes. If you pour salt onto a table, or look at at hour glass running out, you see the same shape. What's going on?

It's a combination of gravity and friction. The grains of sand, rock or ash are pulled down by gravity; they want to flow down-hill. They are, however, also gripped by the other particles already on the slope. This gripping is called friction. Sharp, rough or sticky substances have more friction and this grip force is strong. Smooth or slippery substances are gripped less.

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The friction force is proportional to the normal reaction (the force perpendicular to the direction the object is trying to move), and the limiting ratio of this force to the normal is a dimensionless constant called the coefficient of friction. This is typically given the symbol [size=undefined]μ[/size]

As you can see from the diagram above there is a relationship between the angle of the slope the coefficient of friction. When a particle is dropped onto a slope, if the angle is below a critical angle, it will stay put. If the angle is steeper than a critical angle (defined by the inverse tangent of the coefficient of friction), then it cannot grip and slides down the slope.

It is this behaviour (applied rotationally symmetrically) over the pile that creates the cone shape, and the steepness of the cone is proportional to the coefficient of friction.

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Engineers call this angle the Angle of Repose

The study of friction and the relationship between surfaces moving relative to each other is called Tribology. If you look around, you'll find many examples of the phenomenon.

Fans of Star Wars* will know that the same forces can be applied to an inverted version of the shape. Rather the defining a conical protrusion, the same physics principles can define a conical depression, the slope of which is at the same critical angle.

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Maybe you've experienced this as a child when digging a hole at the beach? As you dig deeper you find that you have to make the diameter of the hole increasingly larger as the sides of the hole continue to collapse. There is a critical angle (which we now know is the Angle of Repose), after which, the walls are no longer able to support the particles and they slide inwards. Wet sand has a higher coefficient of friction than dry sand, so it is possible to dig steeper sided holes in the wet.

There are some clever animals that use this principle to their advantage to catch pray. On of these is the antlion. The antlion larva creates a conical depression in dry sand, and hides at the bottom.

The angle of the sides of the depression are at the angle of repose. An unsuspecting walking insect, such as an ant, when it encounters the slope will slide down into the bottom of the pit; not being able to gain traction to pull itself out, as each attempt to climb up the slope loosens particles the are critically balanced and sends all sliding down to the bottom of the pit and into the waiting jaws of the antlion.

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* “You will, therefore, be taken to the Dune Sea and cast into the Pit of Carkoon, the nesting place of the all powerful Sarlacc.”
— C-3PO's translation of Jabba the Hutt's words to Han Solo, Luke Skywalker, and Chewbacca.

(04-21-2015, 01:53 AM)EA Wrote: Recall:

Land NOT Land

Not Lando

When the sun enters the scene things may or may not change.
depends on pov. That was my first post after post #5050

OSIRIS NAC image of the Aswan new edge taken on 18 May 2016 at 8.40 km far from the 67P nucleus. The spatial scale of the image is 12 cm/pixel. The white arrows show the new sharp edge after the collapse. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDALandslides are not unique to Earth, researchers revealed on Tuesday.

In 2015, Europe's Rosetta spacecraft witnessed—and photographed—a big one on the surface of a comet in deep, dark space, they reported in the journal Nature Astronomy.The cliffside collapse created about 2,000 tonnes of rubble, 99 percent of which settled at the foot of the precipice.The rest was ejected in a spectacular jet of dust.In the first direct evidence for cometary landslides, Rosetta captured before and after images of a wall giving way along a crack 70 metres (230 feet) long and one metre wide on the edge of a cliff named Aswan.Scientists were alerted to the possible collapse in July 2015 by a large plume of dust ejected from comet 67P/Churyumov-Gerasimenko, which Rosetta was orbiting at the time.They traced the jet's origins to Aswan.Five days later, the orbiter's OSIRIS camera observed a "fresh, sharp and bright" edge on the Aswan cliff, where the fracture had been before.The spot—six times brighter than the comet's usual, dusty surface—was the newly-exposed, pristine, icy insides of the comet.

Video representation of the illumination conditions at the Aswan cliff and plateau on 10 July 2015. Credit: M. Pajola et al.The Rosetta mission had observed several previous outbursts, and hypothesised they may be the result of collapsing cliffs.But the study documents "the first unambiguous link between an outburst and a cliff collapse on a comet," the team wrote.Launched in 2004, the European Space Agency's Rosetta spacecraft travelled more than six billion kilometres to reach comet 67P some 400 million kilometres (250 million miles) from Earth.OSIRIS NAC image of the Aswan cliff taken on 26 December 2015 at 77.05 km far from the 67P nucleus. The spatial scale of the image is 1.41 m/pixel. The white arrow shows the bright Aswan cliff with the water ice exposed. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDAIn November 2014, Rosetta released a tiny robot named Philae onto the comet's surface to further probe the alien body.The pair's mission was to unravel the mysteries of life by investigating the comet from all angles.Billions of comets travelling in elliptic orbits around the Sun are believed to be leftovers from the birth of our planetary system some 4.6 billion years ago.NavCam image taken on 10 July 2015 at 156.58 km far from the 67P nucleus. The spatial scale of the image is 15.81 m/pixel. The white arrow shows the outburst caused by the Aswan cliff collapse (in shadow here). Credit: ESA/Rosetta/NavCam – CC BY-SA IGO 3.0On 67P, the Rosetta mission uncovered organic molecules, the building blocks of life.This supported the theory that comets helped spark life on Earth by delivering organic materials when they slammed into our young planet.Water, on the other hand, was unlikely to have come from comets of 67P's type, the mission concluded.OSIRIS NAC image of the Aswan cliff taken on 21 September 2014 at 27.61 km far from the 67P nucleus. The spatial scale of the image is 0.48 m/pixel. The white arrow shows the 70 m long, 1 m wide fracture at the edge of the cliff. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDAExplore further:Image: Rosetta's shadow crosses Comet 67P/Churyumov–Gerasimenko in daring encounterMore information: The pristine interior of comet 67P revealed by the combined Aswan outburst and cliff collapse, Nature Astronomy, nature.com/articles/doi:10.1038/S41550-017-0092

Several sites of cliff collapse on Comet 67P/Churyumov-Gerasimenko were identified during Rosetta's mission. This image focuses on an example in the Ash region, close to the boundary with Imhotep on the comet's large lobe. The yellow arrows mark the fractures where the detachment occurred. The images were taken by Rosetta's OSIRIS camera on Dec. 2, 2014 (left) and March 12, 2016 (right). Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDAA study published March 21, 2017 in the journal Science summarizes the types of surface changes observed during the two years that the European Space Agency's Rosetta spacecraft spent investigating comet 67P/Churyumov-Gerasimenko. Notable differences are seen before and after the comet's most active period—perihelion—when it reached its closest point to the Sun along its orbit.

"Monitoring the comet continuously as it traversed the inner solar system gave us an unprecedented insight not only into how comets change when they travel close to the Sun, but also how fast these changes take place," said Mohamed El-Maarry, a comet researcher at the University of Colorado, Boulder and the lead author of the study.The changes are linked to different geological processes: weathering and erosion, sublimation of water ice, and mechanical stresses arising from the comet's spin."Comet landscapes are fascinating. They are sculpted by slow erosion and dramatic outbursts," said Dennis Bodewits, an assistant research scientist in astronomy at the University of Maryland who is a co-author of the study. "One of the key points of this paper is that the observed changes are small and relatively subtle. Features such as large holes suggest that more violent activity is infrequent on the time scale of an orbital period."Weathering occurs all over the comet, where consolidated materials are weakened—such as by heating and cooling cycles on daily or seasonal timescales—causing their fragmentation. Combined with heating of subsurface ices that lead to outflows of gas, this can ultimately result in the sudden collapse of cliff walls, the evidence of which is apparent in several locations on the comet.A 30-meter-wide, 12,800-ton boulder was found to have moved 140 meters in the Khonsu region of Comet 67P/Churyumov-Gerasimenko in the lead up to perihelion in August 2015, when the comet's activity was at its highest. In both images, an arrow points to the boulder; in the right-hand image, the dotted circle outlines the original location of the boulder for reference. The images were taken by Rosetta's OSIRIS camera on May 2, 2015 (left) and Feb. 7, 2016 (right). Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDAA completely different process is thought to be responsible for a 500-meter-long fracture spotted in August 2014 that runs through the comet's neck in the Anuket region. This fracture was found to have extended by about 30 meters by December 2014. This is linked to the comet's increasing spin rate in the lead up to perihelion. Furthermore, in images taken in June 2016, a new 150 to 300-meter-long fracture was identified parallel to the original fracture.Close to the fractures, a four-meter-wide boulder moved by about 15 meters, as determined by comparing images taken in March 2015 and June 2016. It is not clear whether the fracture extension and movement of the boulder are related to each other or caused by different processes.A substantially larger boulder, some 30 meters wide and weighing 12,800 tons, was found to have moved an impressive 140 meters in the Khonsu region, on the larger of the two comet lobes.

It is thought that the boulder moved during the perihelion period, as several outburst events were detected close to its original position. The movement could have been triggered in one of two ways: either a large amount of underlying material eroded away, allowing the boulder to roll downslope, or a forceful outburst could have directly lifted the boulder to the new location.Erosion caused by the sublimation of material, and deposition of dust falling from outbursts, are also thought to be responsible for sculpting the landscape in different ways. For example, scarps in several smooth plains have been observed to retreat by tens of meters and at a rate of up to a few meters per day around perihelion.Dune-like features that were identified early in Rosetta’s mission in the neck region of Comet 67P/Churyumov–Gerasimenko were seen to evolve over the two years of study (first and last images). In addition, numerous circular scarp-like features were seen to develop and fade over time (central set of images). The circular features reached a diameter of 100 m in less than three months before subsequently fading away again, giving rise to a new set of ripples. The repeated development of these unique features at the same spot is thought to be linked to the curved structure of the neck region directing the flow of sublimating gas in a particular way. The arrows point to the approximately location of the ripple and scarp features to help guide the eye between images when the viewing orientation and resolution changes. The images were taken by Rosetta’s OSIRIS camera on 5 September 2014 (left), 25 April 2015 (centre top left), 10 May 2015 (centre top right), 11 July 2015 (centre bottom left), 20 December 2015 (centre bottom right), and 7 June 2016 (right). The image resolutions are 0.8, 1.6, 2.4, 2.9, 1.7 and 0.5 m/pixel, respectively. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA"Scarp retreats were observed before on Comet Tempel 1, inferred by comparing images taken during flybys of the comet by NASA's Deep Impact in 2005, and Stardust-NExT in 2011," said El-Maarry. "What we were able to do with Rosetta was to monitor similar changes continuously, and at a higher resolution. Our observations additionally tell us that scarp retreat seems to be a common process on comets, specifically in smooth-looking deposits."Furthermore, in the smooth plains of the Imhotep region, previously hidden circular features and small boulders have been exposed by the removal of material. In one location, a depth of about three meters had been removed, most likely through the sublimation of underlying ices.Changes were also noted in the comet's smooth neck region, near distinctive ripples that were likened to Earth's sand dunes when they were first identified. Close monitoring of the ripple formations showed this location to also display expanding circular features in the soft material that reached diameters of 100 meters in less than three months. They subsequently faded away to give rise to new sets of ripples.The researchers speculate that the repeated development of these unique features at the same spot must be linked to the curved structure of the neck region directing the flow of sublimating gas in a particular way.Another type of change is the development of honeycomb-like features noticed in the dusty terrains of the Ma'at region on the comet's small lobe in the northern hemisphere, marked by an increase in surface roughness in the six months leading up to perihelion.Showcase of the different types of changes identified in high-resolution images of Comet 67P/Churyumov–Gerasimenko during more than two years of monitoring by ESA’s Rosetta spacecraft. The approximate locations of each feature are marked on the central context images. Dates of when the ‘before’ and ‘after’ images were taken are also indicated. Note that the orientation and resolution between image pairs may vary, therefore in each image set arrows point to the location of the changes, for guidance. Credit: Top centre images: ESA/Rosetta/NAVCAM, CC BY-SA 3.0 IGO; all others: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDASimilar to other seasonal changes, these features faded substantially after perihelion, presumably as a result of resurfacing by the deposition of new particles ejected from the southern hemisphere during this active period."This documentation of changes over time was a key goal of Rosetta's mission, and shows the surface of comets as geologically active, on both seasonal and short transient timescales," said Matt Taylor, Rosetta project scientist for the European Space Agency.The scientists also note that although many small-scale localized changes have occurred, there were no major shape-changing events that significantly altered the comet's overall appearance. Ground-based observations over the last few decades suggest similar levels of activity during each perihelion, so the researchers think that the major landforms seen during Rosetta's mission were sculpted during a different orbital configuration."At UMD, we use telescopes such as Swift and Spitzer to look at the activity of comets as they approach the Sun for the first time," said Michael A'Hearn, a Distinguished University Professor Emeritus of astronomy at UMD and a co-author on the study. A'Hearn also served as principal investigator on the Deep Impact mission. "We know that such comets are indeed very active. But Rosetta allowed us to see in great detail what this activity did to the surface of comet 67P/Churyumov-Gerasimenko."The research paper, "Surface changes on comet 67P/Churyumov-Gerasimenko suggest a more active past," Mohamed El-Maarry et al., was published March 21, 2017 in the journal Science.A complementary paper, "The pristine interior of comet 67P revealed by the combined Aswan outburst and cliff collapse," by M. Pajola et al, is also published today in Nature Astronomy. Read our news story here.Explore further:Rosetta comet orbiter films deep-space landslideMore information: "Surface changes on comet 67P/Churyumov-Gerasimenko suggest a more active past,", Science, DOI: 10.1126/science.aak9384

Caltech's Konstantinos Giapis has shown how molecular oxygen may be produced on the surface of comets using lab experiments. He and his postdoctoral scholar Yunxi Yao fired high-speed water molecules at oxidized silicon and iron surfaces and observed the production of a plume that included molecular oxygen. Giapis says that similar conditions exist on the comet 67P/Churyumov-Gerasimenko, where the European Space Agency's Rosetta mission detected molecular oxygen. Credit: CaltechA Caltech chemical engineer who normally develops new ways to fabricate microprocessors in computers has figured out how to explain a nagging mystery in space—why comets expel oxygen gas, the same gas we humans breathe.

The discovery that comets produce oxygen gas—also referred to as molecular oxygen or O2—was announced in 2015 by researchers studying the comet 67P/Churyumov-Gerasimenko with the European Space Agency's Rosetta spacecraft. The mission unexpectedly found abundant levels of molecular oxygen in the comet's atmosphere. Molecular oxygen in space is highly unstable, as oxygen prefers to pair up with hydrogen to make water, or carbon to make carbon dioxide. Indeed, O2 has only been detected twice before in space in star-forming nebulas.Scientists have proposed that the molecular oxygen on comet 67P/Churyumov-Gerasimenko might have thawed from its surface after having been frozen inside the comet since the dawn of the solar system 4.6 billion years ago. But questions persist because some scientists say the oxygen should have reacted with other chemicals over all that time.A professor of chemical engineering at Caltech, Konstantinos P. Giapis, began looking at the Rosetta data because the chemical reactions happening on the comet's surface were similar to those he has been performing in the lab for the past 20 years. Giapis studies chemical reactions involving high-speed charged atoms, or ions, colliding with semiconductor surfaces as a means to create faster computer chips and larger digital memories for computers and phones."I started to take an interest in space and was looking for places where ions would be accelerated against surfaces," says Giapis. "After looking at measurements made on Rosetta's comet, in particular regarding the energies of the water molecules hitting the comet, it all clicked. What I've been studying for years is happening right here on this comet."In a new Nature Communications study, Giapis and his co-author, postdoctoral scholar Yunxi Yao, demonstrate in the lab how the comet could be producing oxygen. Basically, water vapor molecules stream off the comet as the cosmic body is heated by the sun. The water molecules become ionized, or charged, by ultraviolet light from the sun, and then the sun's wind blows the ionized water molecules back toward the comet. When the water molecules hit the comet's surface, which contains oxygen bound in materials such as rust and sand, the molecules pick up another oxygen atom from these surfaces and O2 is formed.In other words, the new research implies that the molecular oxygen found by Rosetta need not be primordial after all but may be produced in real time on the comet."We have shown experimentally that it is possible to form molecular oxygen dynamically on the surface of materials similar to those found on the comet," says Yao."We had no idea when we built our laboratory setups that they would end up applying to the astrophysics of comets," says Giapis. "This original chemistry mechanism is based on the seldom-considered class of Eley-Rideal reactions, which occur when fast-moving molecules, water in this case, collide with surfaces and extract atoms residing there, forming new molecules. All necessary conditions for such reactions exist on comet 67P."Other astrophysical bodies, such as planets beyond our solar system, or exoplanets, might also produce molecular oxygen with a similar "abiotic" mechanism—without the need for life. This may influence how researchers search for signs of life on exoplanets in the future."Oxygen is an important molecule, which is very elusive in interstellar space," says astronomer Paul Goldsmith of JPL, which is managed by Caltech for NASA. Goldsmith is the NASA project scientist for the European Space Agency's Herschel mission, which made the first confirmed detection of molecular oxygen in space in 2011. "This production mechanism studied in Professor Giapis's laboratory could be operating in a range of environments and shows the important connection between laboratory studies and astrochemistry."The Nature Communications paper is titled "Dynamic molecular oxygen production in cometary comae."Explore further:Rosetta finds molecular oxygen on comet 67P (Update)Journal reference:Nature CommunicationsProvided by:California Institute of Technology

Quote:"This original chemistry mechanism is based on the seldom-considered class of Eley-Rideal reactions,which occur when fast-moving molecules, water in this case,collide with surfaces and extract atoms residing there, forming new molecules. All necessary conditions for such reactions exist on comet 67P."

As a result of the observations, ROSINA identified seven isotopes of xenon, as well as several isotopes of another noble gas, krypton; these brought to three the inventory of noble gases found at Rosetta's comet, following the discovery of argon from measurements performed in late 2014.The challenging detection, by ESA's Rosetta mission, of several isotopes of the noble gas xenon at Comet 67P/Churyumov-Gerasimenko has established the first quantitative link between comets and the atmosphere of Earth. The blend of xenon found at the comet closely resembles U-xenon, the primordial mixture that scientists believe was brought to Earth during the early stages of Solar System formation.
These measurements suggest that comets contributed about one fifth the amount of xenon in Earth's ancient atmosphere. Xenon - a colourless, odourless gas which makes up less than one billionth of the volume of Earth's atmosphere - might hold the key to answer a long-standing question about comets: did they contribute to the delivery of material to our planet when the Solar System was taking shape, some 4.6 billion years ago? And if so, by how much?
The noble gas xenon is formed in a variety of stellar processes, from the late phases of low- and intermediate-mass stars to supernova explosions and even neutron star mergers. Each of these phenomena gives rise to different isotopes of the element. As a noble gas, xenon does not interact with other chemical species, and is therefore an important tracer of the material from which the Sun and planets originated, which in turns derives from earlier generations of stars.
"Xenon is the heaviest stable noble gas and perhaps the most important because of its many isotopes that originate in different stellar processes: each one provides an additional piece of information about our cosmic origins," says Bernard Marty from CRPG-CNRS and Universite de Lorraine, France. Bernard is the lead author of a paper reporting Rosetta's discovery of xenon at Comet 67P/C-G, which is published in Science.
It is because of this special 'fingerprint' that scientists have been using xenon to investigate the composition of the early Solar System, which provides important clues to constrain its formation. Over the past decades, they sampled the relative abundances of its various isotopes at different locations: in the atmosphere of Earth and Mars, in meteorites deriving from asteroids, at Jupiter, and in the solar wind - the flow of charged particles streaming from the Sun.
The blend of xenon present in the atmosphere of our planet contains a higher abundance of heavier isotopes with respect to the lighter ones; however, this is a result of lighter elements escaping more easily from Earth's gravitational pull and being lost to space in greater amounts. By correcting the atmospheric composition of xenon for this runaway effect, scientists in the 1970s calculated the composition of the primordial mixture of this noble gas, known as U-xenon, that was once present on Earth.
This U-xenon contained a similar mix of light isotopes to that of asteroids and the solar wind, but included significantly smaller amounts of the heavier isotopes.
"For these reasons, we have long suspected that xenon in the early atmosphere of Earth could have a different origin from the average blend of this noble gas found in the Solar System," says Bernard.
One of the explanations is that Solar System xenon derives directly from the protosolar cloud, a mass of gas and dust that gave rise to the Sun and planets, while the xenon found in the Earth's atmosphere was delivered at a later stage by comets, which in turn might have formed from a different mix of material.
With ESA's Rosetta mission visiting Comet 67P/Churyumov-Gerasimenko, an icy fossil of the early Solar System, scientists could finally gather the long-sought data to test this hypothesis.
"Searching for xenon at the comet was one of the most crucial and challenging measurements we performed with Rosetta," says Kathrin Altwegg from the University of Bern, Switzerland, principal investigator of ROSINA, the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis, which was used for this study.
Xenon is very diffuse in the comet's thin atmosphere, so the navigation team had to fly Rosetta very close - 5 km to 8 km from the surface of the nucleus - for a period of three weeks so that ROSINA could obtain a significant detection of all the relevant isotopes.
Flying so close to the comet was extremely challenging because of the large amount of dust that was lifting off the surface at the time, which could confuse the star trackers that were used to orient the spacecraft.
Eventually, the Rosetta team decided to perform this operation in the second half of May 2016. This period was chosen as a compromise so that enough time would have passed after the comet's perihelion, in August 2015, for the dust activity to be less intense, but not too much for the atmosphere to be excessively thin and the presence of xenon hard to detect.
As a result of the observations, ROSINA identified seven isotopes of xenon, as well as several isotopes of another noble gas, krypton; these brought to three the inventory of noble gases found at Rosetta's comet, following the discovery of argon from measurements performed in late 2014.
"These measurements required a long stretch of dedicated time solely for ROSINA, and it would have been very disappointing if we hadn't detected xenon at Comet 67P/C-G, so I'm really glad that we succeeded in detecting so many isotopes," adds Kathrin.
Further analysis of the data revealed that the blend of xenon at Comet 67P/C-G, which contains larger amounts of light isotopes than heavy ones, is quite different from the average mixture found in the Solar System. A comparison with the on-board calibration sample confirmed that the xenon detected at the comet is also different from the current mix in the Earth's atmosphere.

The ESA's Rosetta mission, which ended in September 2016, found that organic matter made up 40% (by mass) of the nucleus of comet 67P Churyumov-Gerasimenko, a.k.a. Chury. Organic compounds, combining carbon, hydrogen, nitrogen, and oxygen, are building blocks of life on Earth. Yet, according to Jean-Loup Bertaux and Rosine Lallement—from the Laboratoire Atmosphères, Milieux, Observations Spatiales (CNRS / UPMC / Université de Versailles Saint-Quentin-en-Yvelines) and the Galaxies, Étoiles, Physique et Instrumentation department of the Paris Observatory (Observatoire de Paris / CNRS / Université Paris Diderot), respectively—these organic molecules were produced in interstellar space, well before the formation of the Solar System. Bertaux and Lallement further assert that astronomers are already familiar with much of this matter.For 70 years, scientists have known that analysis of stellar spectra indicates unknown absorptions, throughout interstellar space, at specific wavelengths called the diffuse interstellar bands (DIBs). DIBs are attributed to complex organic molecules that US astrophysicist Theodore Snow believes may constitute the largest known reservoir of organic matter in the Universe. This interstellar organic material is usually found in the same proportions. However, very dense clouds of matter like presolar nebulae are exceptions. In the middle of these nebulae, where matter is even denser, DIB absorptions plateau or even drop. This is because the organic molecules responsible for DIBs clump together there. The clumped matter absorbs less radiation than when it floated freely in space.Such primitive nebulae end up contracting to form a solar system like our own, with planets . . . and comets. The Rosetta mission taught us that comet nuclei form by gentle accretion of grains progressively greater in size. First, small particles stick together into larger grains. These in turn combine into larger chunks, and so on, until they form a comet nucleus a few kilometers wide.Thus, the organic molecules that formerly populated the primitive nebulae—and that are responsible for DIBs—were probably not destroyed, but instead incorporated into the grains making up cometary nuclei. And there they have remained for 4.6 billion years. A sample-return mission would allow laboratory analysis of cometary organic material and finally reveal the identity of the mysterious interstellar matter underlying observed absorption lines in stellar spectra.If cometary organic molecules were indeed produced in interstellar space—and if they played a role in the emergence of life on our planet, as scientists believe today—might they not also have seeded life on many other planets of our galaxy?Explore further:Rosetta catches dusty organicsMore information: Jean-Loup Bertaux et al, Diffuse Interstellar Bands carriers and cometary organic material., Monthly Notices of the Royal Astronomical Society (2017). DOI: 10.1093/mnras/stx2231Journal reference:Monthly Notices of the Royal Astronomical SocietyProvided by:CNRS

This artist's impression shows the binary asteroid 288P, located in the main asteroid belt between the planets Mars and Jupiter. The object is unique as it is a binary asteroid which also behaves like a comet. The comet-like properties are the result of water sublimation, caused by the heat of the Sun. The orbit of the asteroids is marked by a blue ellipse.

[i]Credit: ESA/Hubble, L. Calçada[/i]

[i]With the help of the NASA/ESA Hubble Space Telescope, a German-led group of astronomers have observed the intriguing characteristics of an unusual type of object in the asteroid belt between Mars and Jupiter: two asteroids orbiting each other and exhibiting comet-like features, including a bright coma and a long tail. This is the first known binary asteroid also classified as a comet. The research is presented in a paper published in the journal [i]Nature today.
[/i][/i]
In September 2016, just before the asteroid 288P made its closest approach to the Sun, it was close enough to Earth to allow astronomers a detailed look at it using the NASA/ESA Hubble Space Telescope [1].
The images of 288P, which is located in the asteroid belt between Mars and Jupiter, revealed that it was actually not a single object, but two asteroids of almost the same mass and size, orbiting each other at a distance of about 100 kilometres. That discovery was in itself an important find; because they orbit each other, the masses of the objects in such systems can be measured.
But the observations also revealed ongoing activity in the binary system. "We detected strong indications of the sublimation of water ice due to the increased solar heating -- similar to how the tail of a comet is created," explains Jessica Agarwal (Max Planck Institute for Solar System Research, Germany), the team leader and main author of the research paper. This makes 288P the first known binary asteroid that is also classified as a main-belt comet.
Understanding the origin and evolution of main-belt comets -- comets that orbit amongst the numerous asteroids between Mars and Jupiter -- is a crucial element in our understanding of the formation and evolution of the whole Solar System. Among the questions main-belt comets can help to answer is how water came to Earth [2]. Since only a few objects of this type are known, 288P presents itself as an extremely important system for future studies.
The various features of 288P -- wide separation of the two components, near-equal component size, high eccentricity and comet-like activity -- also make it unique among the few known wide asteroid binaries in the Solar System. The observed activity of 288P also reveals information about its past, notes Agarwal: "Surface ice cannot survive in the asteroid belt for the age of the Solar System but can be protected for billions of years by a refractory dust mantle, only a few metres thick."
From this, the team concluded that 288P has existed as a binary system for only about 5000 years. Agarwal elaborates on the formation scenario: "The most probable formation scenario of 288P is a breakup due to fast rotation. After that, the two fragments may have been moved further apart by sublimation torques."
The fact that 288P is so different from all other known binary asteroids raises some questions about whether it is not just a coincidence that it presents such unique properties. As finding 288P included a lot of luck, it is likely to remain the only example of its kind for a long time. "We need more theoretical and observational work, as well as more objects similar to 288P, to find an answer to this question," concludes Agarwal.

Notes
[1] Like any object orbiting the Sun, 288P travels along an elliptical path, bringing it closer and further away to the Sun during the course of one orbit.
[2] Current research indicates that water came to Earth not via comets, as long thought, but via icy asteroids.

A final image from Rosetta, shortly before it made a controlled impact onto Comet 67P/Churyumov–Gerasimenko on 30 September 2016, was reconstructed from residual telemetry. The image has a scale of 2 mm/pixel and measures about 1 m across. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDAScientists analysing the final telemetry sent by Rosetta immediately before it shut down on the surface of the comet last year have reconstructed one last image of its touchdown site.

After more than 12 years in space, and two years following Comet 67P/Churyumov–Gerasimenko as they orbited the Sun, Rosetta's historic mission concluded on 30 September with the spacecraft descending onto the comet in a region hosting several ancient pits.It returned a wealth of detailed images and scientific data on the comet's gas, dust and plasma as it drew closer to the surface.But there was one last surprise in store for the camera team, who managed to reconstruct the final telemetry packets into a sharp image."The last complete image transmitted from Rosetta was the final one that we saw arriving back on Earth in one piece moments before the touchdown at Sais," says Holger Sierks, principal investigator for the OSIRIS camera at the Max Planck Institute for Solar System Research in Göttingen, Germany."Later, we found a few telemetry packets on our server and thought, wow, that could be another image."During operations, images were split into telemetry packets aboard Rosetta before they were transmitted to Earth. In the case of the last images taken before touchdown, the image data, corresponding to 23 048 bytes per image, were split into six packets.Annotated image indicating the approximate locations of some of Rosetta’s final images. Note that due to differences in timing and viewing geometry between consecutive images in this graphic, the illumination and shadows vary. Top left: a global view of Comet 67P/Churyumov–Gerasimenko shows the area in which Rosetta touched down in the Ma’at region on the smaller of the two comet lobes. This image was taken by the OSIRIS narrow-angle camera on 5 August 2014 from a distance of 123 km. Top right: an image taken by the OSIRIS narrow-angle camera from an altitude of 5.7 km, during Rosetta’s descent on 30 September 2016. The image scale is about 11 cm/pixel and the image measures about 225 m across. The final touchdown point, named Sais, is seen in the bottom right of the image and is located within a shallow, ancient pit. Exposed, dust-free terrain is seen in the pit walls and cliff edges. Note the image is rotated 180º with respect to the global context image at top right. Middle: an OSIRIS wide-angle camera image taken from an altitude of about 331 m during Rosetta’s descent. The image scale is about 33 mm/pixel and the image measures about 55 m across. The image shows a mix of coarse and fine-grained material. Bottom right: the penultimate image, which was the last complete image taken and returned by Rosetta during its descent, from an altitude of 24.7±1.5 m. Bottom left: the final image, reconstructed after Rosetta’s landing, was taken at an altitude of 19.5±1.5 m. The image has a scale of 2 mm/pixel and measures about 1 m across. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDAFor the very last image the transmission was interrupted after three full packets were received, with 12 228 bytes received in total, or just over half of a complete image. This was not recognised as an image by the automatic processing software, but the engineers in Göttingen could make sense of these data fragments to reconstruct the image.Owing to the onboard compression software, the data were not sent pixel-by-pixel but rather layer-by-layer, which gives an increasing level of detail with each layer.The 53% of transmitted data therefore represents an image with an effective compression ratio of 1:38 compared to the anticipated compression ratio of 1:20, meaning some of the finer detail was lost.That is, it gets a lot blurrier as you zoom in compared with a full-quality image. This can be likened to compressing an image to send via email, versus an uncompressed version that you would print out and hang on your wall.

The camera was not designed to be used below a few hundred metres from the surface but a sharper image could be achieved using the camera in a special configuration: while the camera was designed to be operated with a colour filter in the optical beam, this was removed for the last images. This would have resulted in the images being blurred for the normal imaging scenario above 300 m, but they came into focus at a 'sweet spot' of 15 m distance.Approaching 15 m therefore improved the focus and thus level of detail, as can be seen in the reconstructed image taken from an altitude of 17.9–21.0 m and corresponding to a 1 x 1 m square region on the surface.In the meantime, the altitude of the previously published last image has been revised to 23.3–26.2 m. The uncertainty arises from the exact method of altitude calculation and the comet shape model used.The sequence of images progressively reveals more and more detail of the boulder-strewn surface, providing a lasting impression of Rosetta's touchdown site.Explore further:Image: Rosetta's ever-changing view of a cometProvided by:European Space Agency

"it's actually a gentle process in which the dust agglomerates are not destroyed, but are combined into a larger body with an even greater gravitational attraction - the accumulation of the dust agglomerates into a coherent body is virtually the birth of the comet." Due to the relatively small mass of comet 67P, the pebbles survived intact until today, allowing scientists to confirm the hypothesis for the first time.

Quote: "Now all phases in the planet-formation model have been established", concludes Blum.

Schematic representation of the porous surface structure of comet 67P/Churyumov-Gerasimenko. Based on the results of the Rosetta mission, Blum and colleagues conclude that comet 67P is composed of millimetre-sized dust pebbles. It is assumed that the pebbles inside the comet consist of a mixture of dust and ice (light blue spheres in the image) and only the uppermost layers, which are exposed to direct sunlight, do not contain ice (dark grey spheres). Credit: Maya Krause, TU Braunschweig.The missing link in our understanding of planet formation has been revealed by the first ever spacecraft to orbit and land on a comet, say German scientists. The study is published in a recent edition of the journal Monthly Notices of the Royal Astronomical Society.

A research team led by Jürgen Blum (Technische Universität Braunschweig, Germany) have analysed data from the historic Rosetta mission to uncover how comet 67P/Churyumov-Gerasimenko, or "Chury" for short, came into existence more than four and a half billion years ago.Understanding the evolution of our solar system and its planets was one of the main objectives of the Rosetta mission to comet 67P/Churyumov-Gerasimenko. For Jürgen Blum and his international team it was worth it, because results from the various Rosetta and Philae instruments have revealed that only one out of many proposed models can explain their observations. Comet 67P consists of 'dust pebbles' ranging between millimetres and centimetres in size.Professor Blum explains the implications of the team's observations "Our results show that only a single model for the formation of larger solid bodies in the young solar system may be considered for Chury. According to this formation model, 'dust pebbles' are concentrated so strongly by an instability in the solar nebula that their joint gravitational force ultimately leads to a collapse."This process forms the missing link between the well-established formation of 'dust pebbles' ('planetary building blocks' formed in the solar nebula by sticking collisions between dust and ice particles) and the gravitational accretion of planetesimals into planets, which scientists have pondered over for years."Although it sounds very dramatic" Blum continues, "it's actually a gentle process in which the dust agglomerates are not destroyed, but are combined into a larger body with an even greater gravitational attraction - the accumulation of the dust agglomerates into a coherent body is virtually the birth of the comet." Due to the relatively small mass of comet 67P, the pebbles survived intact until today, allowing scientists to confirm the hypothesis for the first time.In fact, the pebble-collapse formation model can explain many observed properties of comet 67P, for instance its high porosity and how much gas is escaping from inside. "Now all phases in the planet-formation model have been established", concludes Blum.Explore further:Image: Rosetta's ever-changing view of a cometMore information: Jürgen Blum et al, Evidence for the formation of comet 67P/Churyumov-Gerasimenko through gravitational collapse of a bound clump of pebbles, Monthly Notices of the Royal Astronomical Society (2017). DOI: 10.1093/mnras/stx2741Journal reference:Monthly Notices of the Royal Astronomical SocietyProvided by:Royal Astronomical Society

A photo released by the European Space Agency (ESA) in November 2014 shows an image taken by Rosetta's lander Philae on the surface of Comet 67P/Churyumov-GerasimenkoEarth bid a final farewell to robot lab Philae on Wednesday, severing communications after a year-long silence from the pioneering probe hurtling through space on a comet.

Writing an extraordinary chapter in space history, the washing machine-sized craft was the first to land on a comet—primeval rubble from the formation of the Solar System.Philae sent home reams of data garnered from sniffing, tasting and prodding its new alien home hundreds of millions of kilometres (miles) from Earth.Its plucky exploits captured the imagination of children, and many adults, who followed its successes and tribulations via Twitter and an animated cartoon series.But after more than 12 months without news, it was decided to preserve all remaining energy available to Philae's orbiting mothership Rosetta, the European Space Agency (ESA) announced in a blog entitled: "Farewell, silent Philae".Rosetta will remain in orbit around comet 67P/Churyumov-Gerasimenko for another two months.It will crashland on September 30 to join Philae in their final resting place, concluding an historic quest for cometary clues to the origins of life on Earth."Today communication with Philae was stopped," Andreas Schuetz of German space agency DLR told AFP from ground control in Cologne on Wednesday."This is the end of a... fascinating and successful mission for the public and for science."Part of a 1.3-billion-euro ($1.4-billion) ESA mission, Philae was launched into space in March 2004, riding piggyback on Rosetta.The pair travelled some 6.5 billion km (four billion miles)—aided by gravity boosts from Earth and Mars—before entering 67P's orbit in August 2014.Three months later, Rosetta sent the 100-kilogramme (220-pound) probe down to the comet surface—starting a nail-biting deep-space saga.Philae's harpoons failed to fire into the comet surface, and it bounced several times.Abandoning hopeThe tiny robot ended up in a ditch shadowed from the Sun's battery-replenishing rays, but managed to run about 60 hours of experiments and send home valuable data before entering standby mode.As 67P neared the Sun on its elongated orbit, Philae got a battery boost and emerged from hibernation in June 2015, sending a two-minute message via Rosetta, eliciting great excitement on Earth.But after eight intermittent communications, the lander fell permanently silent on July 9, 2015.Rosetta has continued to monitor the comet, but without catching sight of its long-lost charge, even from as close as 10 km away.In February, ground controllers said they believed Philae was in eternal hibernation—though they opted to keep an ear open just in case.Wednesday's final break, at 0900 GMT, means "abandoning all hope of receiving anything more from Philae," said Philippe Gaudon of France's CNES space agency."It's time for me to say goodbye," said Philae's Twitter account, announcing communications "will be switched off forever..."As the comet moves further and further away from the Sun—some 520 million km by end July—Rosetta needs to save energy for her final weeks."We need to maximise the power available to Rosetta's scientific instruments, and thus had no choice but to turn off the ESS," ESA senior science advisor Mark McCaughrean told AFP.The ESS is the Electrical Support System on board Rosetta, used to send home the results of Philae's science experiments and status reports."The power will only dwindle further, and so now the focus turns fully to Rosetta, whose amazingly succesful scientific mission will come to an end on 30 September," said McCaughrean."Everyone involved will be extremely sad, of course, but equally enormously proud of what has been achieved by this unique space mission."Scientists will be busy for years analysing the data sent back by Philae and Rosetta.Comets are deemed to be balls of primitive dust and ice left from the early years of the Solar System.Their makeup interests scientists who speculate that comets may have seeded Earth—possibly other planets as well—with the ingredients for life.

An artist’s conception of a view from within the Exocomet system KIC 3542116. Credit: Danielle FutselaarScientists from MIT and other institutions, working closely with amateur astronomers, have spotted the dusty tails of six exocomets—comets outside our solar system—orbiting a faint star 800 light years from Earth.

These cosmic balls of ice and dust, which were about the size of Halley's Comet and traveled about 100,000 miles per hour before they ultimately vaporized, are some of the smallest objects yet found outside our own solar system.The discovery marks the first time that an object as small as a comet has been detected using transit photometry, a technique by which astronomers observe a star's light for telltale dips in intensity. Such dips signal potential transits, or crossings of planets or other objects in front of a star, which momentarily block a small fraction of its light.In the case of this new detection, the researchers were able to pick out the comet's tail, or trail of gas and dust, which blocked about one-tenth of 1 percent of the star's light as the comet streaked by."It's amazing that something several orders of magnitude smaller than the Earth can be detected just by the fact that it's emitting a lot of debris," says Saul Rappaport, professor emeritus of physics in MIT's Kavli Institute for Astrophysics and Space Research. "It's pretty impressive to be able to see something so small, so far away."Rappaport and his team have published their results this week in the Monthly Notices of the Royal Astronomical Society. The paper's co-authors are Andrew Vanderburg of the Harvard-Smithsonian Center for Astrophysics; several amateur astronomers including Thomas Jacobs of Bellevue, Washington; and researchers from the University of Texas at Austin, NASA's Ames Research Center, and Northeastern University."Where few have traveled"The detection was made using data from NASA's Kepler Space Telescope, a stellar observatory that was launched into space in 2009. For four years, the spacecraft monitored about 200,000 stars for dips in starlight caused by transiting exoplanets.To date, the mission has identified and confirmed more than 2,400 exoplanets, mostly orbiting stars in the constellation Cygnus, with the help of automated doink-head that quickly sift through Kepler's data, looking for characteristic dips in starlight.

The smallest exoplanets detected thus far measure about one-third the size of the Earth. Comets, in comparison, span just several football fields, or a small city at their largest, making them incredibly difficult to spot.However, on March 18, Jacobs, an amateur astronomer who has made it his hobby to comb through Kepler's data, was able to pick out several curious light patterns amid the noise.Jacobs, who works as an employment consultant for people with intellectual disabilities by day, is a member of the Planet Hunters—a citizen scientist project first established by Yale University to enlist amateur astronomers in the search for exoplanets. Members were given access to Kepler's data in hopes that they might spot something of interest that a computer might miss.In January, Jacobs set out to scan the entire four years of Kepler's data taken during the main mission, comprising over 200,000 stars, each with individual light curves, or graphs of light intensity tracked over time. Jacobs spent five months sifting by eye through the data, often before and after his day job, and through the weekends."Looking for objects of interest in the Kepler data requires patience, persistence, and perseverance," Jacobs says. "For me it is a form of treasure hunting, knowing that there is an interesting event waiting to be discovered. It is all about exploration and being on the hunt where few have traveled before.""Something we've seen before"Jacobs' goal was to look for anything out of the ordinary that computer doink-head may have passed over. In particular, he was searching for single transits—dips in starlight that happen only once, meaning they are not periodic like planets orbiting a star multiple times.In his search, he spotted three such single transits around KIC 3542116, a faint star located 800 light years from Earth (the other three transits were found later by the team). He flagged the events and alerted Rappaport and Vanderburg, with whom he had collaborated in the past to interpret his findings."We sat on this for a month, because we didn't know what it was—planet transits don't look like this," Rappaport recalls. "Then it occurred to me that, 'Hey, these look like something we've seen before.'"In a typical planetary transit, the resulting light curve resembles a "U," with a sharp dip, then an equally sharp rise, as a result of a planet first blocking a little, then a lot, then a little of the light as it moves across the star. However, the light curves that Jacobs identified appeared asymmetric, with a sharp dip, followed by a more gradual rise.Rappaport realized that the asymmetry in the light curves resembled disintegrating planets, with long trails of debris that would continue to block a bit of light as the planet moves away from the star. However, such disintegrating planets orbit their star, transiting repeatedly. In contrast, Jacobs had observed no such periodic pattern in the transits he identified."We thought, the only kind of body that could do the same thing and not repeat is one that probably gets destroyed in the end," Rappaport says.In other words, instead of orbiting around and around the star, the objects must have transited, then ultimately flown too close to the star, and vaporized."The only thing that fits the bill, and has a small enough mass to get destroyed, is a comet," Rappaport says.The researchers calculated that each comet blocked about one-tenth of 1 percent of the star's light. To do this for several months before disappearing, the comet likely disintegrated entirely, creating a dust trail thick enough to block out that amount of starlight.Vanderburg says the fact that these six exocomets appear to have transited very close to their star in the past four years raises some intriguing questions, the answers to which could reveal some truths about our own solar system."Why are there so many comets in the inner parts of these solar systems?" Vanderburg says. "Is this an extreme bombardment era in these systems? That was a really important part of our own solar system formation and may have brought water to Earth. Maybe studying exocomets and figuring out why they are found around this type of star … could give us some insight into how bombardment happens in other solar systems."The researchers say that in the future, the MIT-led Transiting Exoplanet Survey Satellite (TESS) mission will continue the type of research done by Kepler.Apart from contributing to the fields of astrophysics and astronomy, Rappaport says, the new detection speaks to the perserverence and discernment of citizen scientists."I could name 10 types of things these people have found in the Kepler data that doink-head could not find, because of the pattern-recognition capability in the human eye," Rappaport says. "You could now write a computer doink-headto find this kind of comet shape. But they were missed in earlier searches. They were deep enough but didn't have the right shape that was programmed into doink-head. I think it's fair to say this would never have been found by any algorithm."This research made use of data collected by the Kepler mission, funded by the NASA Science Mission directorate.Explore further:Finding a 'lost' planet, about the size of Neptune

Astronomers capture first visiting object from outside our solar system

October 27, 2017

Credit: Queen's University BelfastA Queen's University Belfast scientist is leading an international team in studying a new visitor to our solar system - the first known comet or asteroid to visit us from another star.

The fast-moving object, now named A/2017 U1, was initially spotted on 18 October in Hawaii by the Pan-STARRS 1 telescope in Hawaii. Professor Alan Fitzsimmons from the School of Mathematics and Physics at Queen's, together with colleagues in the UK, USA and Chile have been tracking it using powerful telescopes across the world.Commenting on the project, Professor Fitzsimmons said: "By Wednesday this week it became almost certain this object was alien to our solar system. We immediately started studying it that night with the William Herschel Telescope in the Canary Islands, then on Thursday night with the Very Large Telescope in Chile."The initial data implies it is a small rocky or icy object that may have been drifting through our galaxy for millions or even billions of years, before entering our solar system by chance. The object flew into the solar system from above, was close to the Sun last month, and is now already on its way back out to the stars.Astronomers believe it was probably thrown out of another star system during a period of planet formation. The same process is thought to have unfolded 4.5 billion years ago around our own star, when Jupiter and Saturn formed. Despite suspecting such objects existed and looking out for them over past decades, scientists have never seen such an interstellar visitor until now.Credit:During rapid investigations, Professor Fitzsimmons' team has now captured clear images of the unusual object, and obtained data on its possible chemical makeup.Meabh Hyland, a PhD student from the Astrophysics Research Centre at Queen's University Belfast, said: "It's wonderful and exciting to see this object passing through our planetary system."Commenting on the incredible findings, Professor Fitzsimmons added: "It sends a shiver down the spine to look at this object and think it has come from another star."Credit: Queen's University BelfastMore information is needed to pin down the exact details of where the visitor came from and what its properties are, but luckily the object should be visible in powerful telescopes for a few more weeks, allowing scientists to continue their investigations.

Left: The surface of Rosetta’s comet. As the comet approaches the Sun, frozen gases evaporate from below the surface, dragging tiny particles of dust along with them. Right: These dust grains can be captured and examined using the COSIMA …more
The dust that comet 67P/Churyumov-Gerasimenko emits into space consists to about one half of organic molecules. The dust belongs to the most pristine and carbon-rich material known in our solar system and has hardly changed since its birth. These results of the COSIMA team are published today in the journal Monthly Notices of the Royal Astronomical Society. COSIMA is an instrument onboard the Rosetta spacecraft, which investigated comet 67P/Churyumov-Gerasimenko from August 2014 to September 2016. In their current study, the involved researchers including scientists from the Max Planck Institute for Solar System Research (MPS) analyze as comprehensively as ever before, what chemical elements constitute cometary dust.

"Of course, Rosetta's comet contains water like any other comet, too," says Hilchenbach. "But because comets have spent most of their time at the icy rim of the solar system, it has almost always been frozen and could not react with the minerals." The researchers therefore regard the lack of hydrated minerals in the comet's dust as an indication that 67P contains very pristine material.
This conclusion is supported by the ratio of certain elements such as carbon to silicon. With more than 5, this value is very close to the Sun's value, which is thought to reflect the ratio found in the early solar system.
The current findings also touch on our ideas of how life on Earth came about. In a previous publication, the COSIMA team was able to show that the carbon found in Rosetta's comet is mainly in the form of large, organic macromolecules. Together with the current study, it becomes clear that these compounds make up a large part of the cometary material. Thus, if comets indeed supplied the early Earth with organic matter, as many researchers assume, it would probably have been mainly in the form of such macromolecules.Explore further:Rosetta catches dusty organicsMore information: Anaïs Bardyn et al. Carbon-rich dust in comet 67P/Churyumov-Gerasimenko measured by COSIMA/Rosetta, Monthly Notices of the Royal Astronomical Society (2017). DOI: 10.1093/mnras/stx2640

Dragonfly would visit several locations tens and even hundreds of miles apart to study Titan's surface and atmosphere. It could explore in depth some of the places where satellites such as NASA's Cassini spacecraft (may it rest in peace) have gotten only a distant glimpse.
Dragonfly is a dual-quadcopter lander that would take advantage of the environment on Titan to fly to multiple locations, some hundreds of miles apart, to sample materials and determine surface composition to investigate Titan's organic chemistry and habitability, monitor atmospheric and surface conditions, image landforms to investigate geological processes, and perform seismic studies. Credit: NASA
Like CAESAR, Dragonfly would be making a repeat visit: Cassini's Huygens probe landed on Titan in 2005 and studied the surface for less than a day. The robo-copter would take those studies much further, analyzing the moon's organic chemistry and habitability and the geological processes at play.
"In this way we can evaluate how far prebiotic chemistry has progressed in an environment that we know has the ingredients for life—for water-based life or potentially even hydrocarbon-based life," Turtle said.
These two missions have been selected for what's called a Phase A concept study, Green said. The mission teams' final proposals would be due in January 2019 and NASA would likely pick the winner that July. The winner would be slated for launch in the mid-2020s.
Whichever mission makes it to the launchpad will have big figurative shoes to fill. The last three New Frontiers missions were the New Horizons mission to Pluto, the Juno mission to Jupiter and the OSIRIS-REx mission now en route to the asteroid Bennu (and set to arrive in August 2018).Explore further:APL proposes Dragonfly mission to explore potential habitable sites on Saturn's largest moonRE:Ducks
67p ANU Mission to "bring back some quantum-quack"The CAESAR (Comet Astrobiology Exploration SAmple Return) mission will acquire a sample from the nucleus of comet Churyumov-Gerasimenko, returning it safely to Earth.Redux

...
They have to go to Titan,
but they won't,
it's easier to make the comet mission happen.
We have seen a comet up close.
In our lifetimes we won't get another chance at Titan.
Not to mention Venus.
...

The final stage of a simulation, carried out by the authors, of a catastrophic collision between comets, showing one of the objects formed by re-accretion of debris from the collision, with a shape identical to that of Chury. Credit: ESA/Rosetta/Navcam - CC BY-SA IGO 3.0

Comets which consist of two parts, like Chury, can form after a catastrophic collision of larger bodies. Such collisions may have taken place in a later phase of our solar system, which suggests that Chury can be much younger than previously assumed. This is shown through computer simulations by an international research group with the participation of the University of Bern.

In the computer simulations, the research team investigated what happened after two large comet nuclei violently collided together. "The calculations showed that a large part of the material accumulates in many smaller bodies," explains Martin Jutzi of the Center for Space and Habitability (CSH) at the University of Bern and member of the National Centre of Competence in Research PlanetS. The newly created objects have different sizes and shapes, among them are many elongated bodies, some of which consist of two parts, just like the comet 67P/Churyumov-Gerasimenko, which the University of Bern studied in detail with the Bern mass spectrometer ROSINA on the Rosetta spacecraft.
"We were surprised that in such catastrophic collisions only a small part of the material is considerably compressed and heated," says Martin Jutzi. Moreover, this material is then ejected and hardly contributes to the formation of the smaller bodies that form a new generation of comet nuclei. On the side of the comet opposite the impact point, volatile substances can withstand even violent collisions. This is why the new generation of comets still has a low density and is rich in volatile substances—properties which have also been found on the comet Chury. Therefore, the duck-shaped comet may well have emerged after a violent, late collision and did not necessarily have to originate from the early formation phase of the solar system, as has been claimed repeatedly. Such collisions could have taken place relatively late in the life of the solar system. This finding has been reported in the journal Nature Astronomy by the research group led by Stephen Schwartz from the University of Côte d' Azur and the University of Arizona.

Simulations of comet collions. Credit: Université Côte d’Azur/University of BernImpact with a velocity of several kilometers per second
In previous studies, Martin Jutzi and Willy Benz, astrophysicist at CSH of the University of Bern and PlanetS director, had already come to the conclusion that Chury did not receive its two-component structure when our solar system was formed 4.5 billion years ago. The researchers showed that the weak point between the two parts of the comet could not have lasted for several billion years and that Chury may have been created by a comparatively gentle impact. "We have now investigated catastrophic collisions involving a lot more energy," explains Martin Jutzi. The new calculations confirm the previous results and extend the possible formation scenarios.

The research team investigated what happens when different sized bodies collide at different angles at speeds ranging from 20 to 3,000 meters per second. The simulations showed that small fragments merge into many transient aggregates in the hours and days after the collision (see video). The final shape is often the result of two or more large bodies that collide at very low speeds to form a two-component structure.
Comet Chury taken by the Rosetta spacecraft. Credit: ESA/Rosetta/Navcam - CC BY-SA IGO 3.0

Possible explanation for "Chury's" mysterious structures
According to the simulations, during the days and weeks in which the comet received its shape, small aggregates in the vicinity continue to reaccumulate onto it. In reality, this material could be flattened when it hits the surface and thus lead to a layered structure. Moreover, if large blocks accumulate at this stage, cavities may be created which can develop into large pits. Such geological structures were discovered on Chury by the Rosetta mission – these observations were previously considered mysterious. "Our results not only confirm that the comet Chury may be much younger than previously assumed, but also provide a possible explanation for its striking structures," says Jutzi.

Ugly ducklings: should rubber ducks be banned from the bath?
March 27, 2018

Dark side of bath toys. Credit: Andri Bryner, Eawag

Scientific curiosity knows no bounds: a group of Swiss and US researchers have delved into "the dark side" of inviting rubber ducks and other flexible plastic toys into our tubs.

Any plastic materials dunked in bathwater provide ideal conditions for bacterial and fungal growth, according to the conclusions of the joint study, published Tuesday by the Swiss government.
"Dense growths of bacteria and fungi are found on the inner surface of these flexible toys, and a murky liquid will often be released when they are squeezed by a child," the Swiss government statement said.
The researchers from the Swiss Federal Institute of Aquatic Science and Technology EAWAG, the Swiss Federal Polytechnic School and the University of Illinois found that "diverse microbial growth is promoted not only by the plastic materials but by bath users themselves."
For their study, they carried out experiments with real bath toys and controls using new bath toys under conditions simulating household use.
Over a period of 11 weeks, they exposed some of the toys to clean and others to dirty bath water, containing things like soap and body fluids.
When they cut open the toys, "the findings sound unappetising: between five million and 75 million cells per square centimetre were observed on the inner surfaces," according to the summary of the report.
The researchers stressed though that there was a big difference between the plastic toys exposed to different types of water.
"Fungal species were detected in almost 60 percent of the real bath toys and in all the dirty-water control toys," the statement said.
"Potentially pathogenic bacteria were identified in 80 percent of all the toys studied, including Legionella and Pseudomonas aeruginosa," which is often the culprit in hospital-acquired infections, it added.
The main problem is that warm water gathers inside the toy, often made of low-quality polymers, which release organic carbon compounds that serve as nutrients to growing bacteria colonies.
"During bathing, other key nutrients such as nitrogen and phosphorus, as well as additional bacteria, are contributed by the human body (body fluids such as urine and sweat), external contaminants and personal care products," according to the study.
This allows bacteria and fungi to multiply inside of a toy children often enjoy using to squirt water into their faces.
"This could strengthen the immune system, which would be positive, but it can also result in eye, ear, or even gastrointestinal infections," microbiologist Frederik Hammes pointed out in Tuesday's statement.
So should we toss the ducks out with the bathwater? Or as some suggest on Internet comment forums, simply plug their holes to avoid the accumulation in their cavity?
Hammes suggests a more scientific approach: tighter regulations on the polymeric materials used to produce bath toys.[/url] More information: Lisa Neu et al. Ugly ducklings—the dark side of plastic materials in contact with potable water, npj Biofilms and Microbiomes (2018). [url=http://dx.doi.org/10.1038/s41522-018-0050-9]DOI: 10.1038/s41522-018-0050-9

Along the vines of the Vineyard.
With a forked tongue the snake singsss...

Far from the Sun, comets are lifeless, ice-cold bodies. When they progress into the inner solar system, they become active: frozen gases such as water evaporate and entrain dust particles from the surface. In this way the coma, a shroud of gas and dust, is formed. Already in images from earlier cometary missions such as Giotto, which flew by comet 1P/Halley in 1986, distinct jets of gas and dust were visible within the coma. They reach up to several kilometers into space. For scientists, these jets are the key to cometary activity. When and where do they occur? Which processes on the surface are involved? And what do they reveal about the nature and composition of the comet?

No mission has been able to pursue these questions in as great detail as ESA's Rosetta mission. From August 2014 to September 2016, the Rosetta spacecraft orbited comet 67P/Churyumov-Gerasimenko witnessing its transformation from an almost lifeless to a gas- and dust-spewing body from close-up. More than 70 000 images taken by the scientific camera system OSIRIS, which was developed and built under the leadership of MPS, document this process. They contain both eruptive, sudden outbursts of gas and dust, as well as jets that are stable for a longer time. In their most recent publication, researchers from the OSIRIS team have now investigated the activity that occurs regularly every morning.

"When the Sun rises over a part of the comet, the surface along the terminator almost instantaneously becomes active," first author Dr. Xian Shi from MPS describes. "The jets of gas and dust, which we then observe within the coma, are very reliable: they are found each morning in the same places and in a similar form," she adds. Responsible for this early morning activity is the frost, which forms at night on the cold comet surface. As soon as the Sun's rays touch it, it begins to evaporate.

"Outbursts can often be traced back to a small area on the surface where suddenly frozen water is exposed, for example due to a landslide," explains Dr. Holger Sierks from the MPS, OSIRIS Principal Investigator. "In the case of cometary activity at sunrise, this is different. The frost is distributed fairly evenly over the entire surface." But then why do the gas and dust emissions form jets? Why do they not create a completely homogeneous cloud?

Quote:The new analysis is consistent with team's original conclusion, that molecular oxygen is most likely primordial. Other theories have been proposed, and can't yet be ruled out, but the primordial theory currently fits the data best.

Molecular oxygen in comet's atmosphere not created on its surface
July 3, 2018 by Hayley Dunning, Imperial College London

View of comet 67P taken by Rosetta. Credit: European Space Agency
Scientists have found that molecular oxygen around comet 67P is not produced on its surface, as some suggested, but may be from its body.

The European Space Agency's Rosetta spacecraft escorted comet 67P/Churyumov-Gerasimenko on its journey round the sun from August 2014—September 2016, dropping a probe and eventually crashing onto its surface.

When the comet is close enough to the sun the ice on its surface 'sublimes' - transforms from solid to gas—forming a gas atmosphere called a coma. Analysis of the coma by instruments on Rosetta revealed that it contained not only water, carbon monoxide and carbon dioxide, as anticipated, but also molecular oxygen.

Molecular oxygen is two oxygen atoms joined together, and on Earth it is essential for life, where it is produced by photosynthesis. It has been previously detected around some of the icy moons of Jupiter, but it was not expected to be found around a comet.

The Rosetta science team originally reported that the oxygen was most likely from the comet's main body, or nucleus. This meant it was 'primordial' - that it was already present when the comet itself formed at the beginning of the Solar System 4.6 billion years ago.

One group of outside researchers however suggested there might be a different source for molecular oxygen at comets. They had discovered a new way to produce molecular oxygen in space triggered by energetic ions—electrically charged molecules. They proposed that reactions with energetic ions on the surface of comet 67P could instead be the source of the detected molecular oxygen.

Views of the comet form Rosetta. Credit: ESA
Now, members of the Rosetta team have analysed the data on 67P's oxygen in light of the new theory. In a paper published today in Nature Communications and led by Imperial College London physicists, they report that the proposed mechanism for producing oxygen on the surface of the comet is not sufficient to explain the observed levels in the coma.

Lead author Mr Kevin Heritier, from the Department of Physics at Imperial, said: "The first detection of molecular oxygen in 67P's coma was both very surprising and exciting".

"We tested the new theory of surface molecular oxygen production using observations of energetic ions, particles which trigger the surface processes which could lead to the production of molecular oxygen. We found that the amount of energetic ions present could not produce enough molecular oxygen to account for the amount of molecular oxygen observed in the coma."

Co-author Dr. Marina Galand, from the Department of Physics at Imperial and Science Co-Investigator of the Rosetta Plasma Consortium, added: "Surface generation of molecular oxygen may still happen on 67P, but the majority of the molecular oxygen in the coma is not produced through such a process."

The new analysis is consistent with team's original conclusion, that molecular oxygen is most likely primordial. Other theories have been proposed, and can't yet be ruled out, but the primordial theory currently fits the data best.

This is also supported by recent theories which revisited the formation of the molecular oxygen in dark clouds and the presence of molecular oxygen in the early Solar System. In this model, molecular oxygen created froze onto small dust grains. These grains collected more material, eventually building up the comet and locking the oxygen in the nucleus.

[size=undefined]Sep 12, 2013 - You can see bow shocks also in front of a swimming swan/duck, etc. Or just move your hand strongly through still water and get a shock wave ...[/size]waves - Why is the angle of the wake of a duck constant? - Physics ...

[size=undefined]4 answersMay 6, 2011 - The Kelvin wake does not describe the narrow turbulent band behind a ship, nor shock waves. The Kelvin wake consists of two types of waves: ...
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A new study reveals that, contrary to first impressions, Rosetta did detect signs of an infant bow shock at the comet it explored for two years – the first ever seen forming anywhere in the solar system.

From 2014 to 2016, ESA's Rosetta spacecraft studied Comet 67P/Churyumov-Gerasimenko and its surroundings from near and far. It flew directly through the 'bow [url=https://phys.org/tags/shock/]shock' several times both before and after the comet reached its closest point to the sun along its orbit, providing a unique opportunity to gather in situ measurements of this intriguing patch of space.

Comets offer scientists an extraordinary way to study the plasma in the solar system. Plasma is a hot, gaseous state of matter comprising charged particles, and is found in the solar system in the form of the solar wind: a constant stream of particles flooding out from our star into space.

As the supersonic solar wind flows past objects in its path, such as planets or smaller bodies, it first hits a boundary known as a bow shock. As the name suggests, this phenomenon is somewhat like the wave that forms around the bow of a ship as it cuts through choppy water. Bow shocks have been found around comets, too – Halley's comet being a good example. Plasma phenomena vary as the medium interacts with the surrounding environment, changing the size, shape, and nature of structures such as bow shocks over time.

Rosetta looked for signs of such a feature over its two-year mission, and ventured over 1500 km away from 67P's centre on the hunt for large-scale boundaries around the comet – but apparently found nothing.

Simulated view of Rosetta spying an infant bow shock at the comet. Click here for details and large versions of the video. Credit: ESA/Rosetta/RPC; H. Gunell et al (2018)"We looked for a classical bow shock in the kind of area we'd expect to find one, far away from the comet's nucleus, but didn't find any, so we originally reached the conclusion that Rosetta had failed to spot any kind of shock," says Herbert Gunell of the Royal Belgian Institute for Space Aeronomy, Belgium, and Umeå University, Sweden, one of the two scientists who led the study.

"However, it seems that the spacecraft actually did find a bow shock, but that it was in its infancy. In a new analysis of the data, we eventually spotted it around 50 times closer to the comet's nucleus than anticipated in the case of 67P. It also moved in ways we didn't expect, which is why we initially missed it."

On 7 March 2015, when the comet was over twice as far from the sun as the Earth and heading inwards towards our star, Rosetta data showed signs of a bow shock beginning to form. The same indicators were present on its way back out from the sun, on 24 February 2016. This boundary was observed to be asymmetric, and wider than the fully developed bow shocks observed at other comets.

"Such an early phase of the development of a bow shock around a comet had never been captured before Rosetta," says co-lead Charlotte Goetz of the Institute for Geophysics and Extraterrestrial Physics in Braunschweig, Germany.

"The infant shock we spotted in the 2015 data will have later evolved to become a fully developed bow shock as the comet approached the sun and became more active – we didn't see this in the Rosetta data, though, as the spacecraft was too close to 67P at that time to detect the 'adult' shock. When Rosetta spotted it again, in 2016, the comet was on its way back out from the sun, so the shock we saw was in the same state but 'unforming' rather than forming."

Key moments in Rosetta's first year at comet 67P/Churyumov-Gerasimenko. Credit: European Space AgencyHerbert, Charlotte, and colleagues explored data from the Rosetta Plasma Consortium, a suite of instruments comprising five different sensors to study the plasma surrounding Comet 67P. They combined the data with a plasma model to simulate the comet's interactions with the solar wind and determine the properties of the bow shock.

The scientists found that, when the forming bow shock washed over Rosetta, the comet's magnetic field became stronger and more turbulent, with bursts of highly energetic charged particles being produced and heated in the region of the shock itself. Beforehand, particles had been slower-moving, and the solar wind had been generally weaker – indicating that Rosetta had been 'upstream' of a bow shock.

"These observations are the first of a bow shock before it fully forms, and are unique in being gathered on-location at the comet and shock itself," says Matt Taylor, ESA Rosetta Project Scientist.

"This finding also highlights the strength of combining multi-instrument measurements and simulations. It may not be possible to solve a puzzle using one dataset, but when you bring together multiple clues, as in this study, the picture can become clearer and offer real insight into the complex dynamics of our solar system – and the objects in it, like 67P."

Single frame enhanced NavCam image taken on 27 March 2016, when Rosetta was 329 km from the nucleus of Comet 67P/Churyumov-Gerasimenko. The scale is 28 m/pixel and the image measures 28.7 km across. Credit: ESA/Rosetta/NavCam – CC BY-SA IGO 3.0Feeling stressed? You're not alone. ESA's Rosetta mission has revealed that geological stress arising from the shape of Comet 67P/Churyumov–Gerasimenko has been a key process in sculpting the comet's surface and interior following its formation.

Small, icy comets with two distinct lobes seem to be commonplace in the solar system, with one possible mode of formation a slow collision of two primordial objects in the early stages of formation some 4.5 billion years ago. A new study using data collected by Rosetta during its two years at Comet 67P/C-G has illuminated the mechanisms that contributed to shaping the comet over the following billions of years.

The researchers used stress modelling and three-dimensional analyses of images taken by Rosetta's high resolution OSIRIS camera to probe the comet's surface and interior.

"We found networks of faults and fractures penetrating 500 metres underground, and stretching out for hundreds of metres," says lead author Christophe Matonti of Aix-Marseille University, France.

"These geological features were created by shear stress, a mechanical force often seen at play in earthquakes or glaciers on Earth and other terrestrial planets, when two bodies or blocks push and move along one another in different directions. This is hugely exciting: it reveals much about the comet's shape, internal structure, and how it has changed and evolved over time."

These images show how Rosetta’s dual-lobed comet, 67P/Churyumov-Gerasimenko, has been affected by a geological process known as mechanical shear stress. The comet’s shape is shown in the left two diagrams from top and side perspectives, …moreThe model developed by the researchers found shear stress to peak at the centre of the comet's 'neck', the thinnest part of the comet connecting the two lobes.

"It's as if the material in each hemisphere is pulling and moving apart, contorting the middle part – the neck – and thinning it via the resulting mechanical erosion," explains co-author Olivier Groussin, also of Aix-Marseille University, France.

"We think this effect originally came about because of the comet's rotation combined with its initial asymmetric shape. A torque formed where the neck and 'head' meet as these protruding elements twist around the comet's centre of gravity."

The observations suggest that the shear stress acted globally over the comet and, crucially, around its neck. The fact that fractures could propagate so deeply into 67P/C-G also confirms that the material making up the interior of the comet is brittle, something that was previously unclear.

"None of our observations can be explained by thermal processes," adds co-author Nick Attree of the University of Stirling, UK. "They only make sense when we consider a shear stress acting over the entire comet and especially around its neck, deforming and damaging and fracturing it over billions of years."

This diagram illustrates the evolution of Rosetta’s dual-lobed comet, 67P/Churyumov-Gerasimenko, over the past 4.5 billion years. Credit: C. Matonti et al (2019)Sublimation, the process of ices turning to vapour and resulting in comet dust being dragged out into space, is another well-known process that can influence a comet's appearance over time. In particular, when a comet passes closer to the Sun, it warms up and loses its ices more rapidly – perhaps best visualised in some of the dramatic outbursts captured by Rosetta during its time at Comet 67P/C–G.

The new results shed light on how dual-lobe comets have evolved over time.

Comets are thought to have formed in the earliest days of the solar system, and are stored in vast clouds at its outer edges before beginning their journey inwards. It would have been during this initial 'building' phase of the solar system that 67P/C-G got its initial shape.

The new study indicates that, even at large distances from the Sun, shear stress would then act over a timescale of billions of years following formation, while sublimation erosion takes over on shorter million-year timescales to continue shaping the comet's structure – especially in the neck region that was already weakened by shear stress.

Excitingly, NASA's New Horizons probe recently returned images from its flyby of Ultima Thule, a trans-Neptunian object located in the Kuiper belt, a reservoir of comets and other minor bodies at the outskirts of the solar system.

First impressions of the Kuiper Belt object Ultima Thule (left) revealed a surprisingly familiar appearance to the comet that ESA's Rosetta spacecraft explored for more than two years (right). Credit: Left: NASA/Johns Hopkins University …moreThe data revealed that this object also has a dual-lobed shape, even though somewhat flattened with respect to Rosetta's comet.

"The similarities in shape are promising, but the same stress structures don't seem to be apparent in Ultima Thule," comments Christophe.Ultima Thule ???

As more detailed images are returned and analysed, time will tell if it has experienced a similar history to 67P/C-G or not."Comets are crucial tools for learning more about the formation and evolution of the solar system," says Matt Taylor, ESA's Rosetta Project Scientist.

"We've only explored a handful of comets with spacecraft, and 67P is by far the one we've seen in most detail. Rosetta is revealing so much about these mysterious icy visitors and with the latest result we can study the outer edges and earliest days of the solar system in a way we've never been able to do before."

This single frame Rosetta navigation camera image of Comet 67P/Churyumov-Gerasimenko was taken on 7 July 2015 from a distance of 154 km from the comet centre. Credit: ESA/Rosetta/NAVCAM
All comets might share their place of birth, new research says. For the first time ever, astronomer Christian Eistrup applied chemical models to fourteen well-known comets, surprisingly finding a clear pattern. His publication has been accepted in the journal Astronomy & Astrophysics.

[b]Comets: balls of ice or more?[/b]
Comets travel through our solar system and are composed of ice, dust, and small rock-like particles. Their nuclei can be as large as tens of kilometers across. "Comets are everywhere, and sometimes with very funky orbits around the Sun. In the past, comets even have hit the Earth," Christian Eistrup says. "We know what comets consist of and which molecules are present in them. They vary in composition, but are normally seen as just one group of icy balls. Therefore, I wanted to know whether comets are indeed one group, or whether different subsets can be made."[b]A new take on comets[/b]
"What if I apply our existing chemical models to comets?", Eistrup thought during his Ph.D. at Leiden University. In the research team at Leiden Observatory, which included Kavli Prize winner Ewine van Dishoeck, he developed models to predict the chemical composition of protoplanetary discs—flat discs of gas and dust encompassing young stars. Understanding these discs can give insight into how stars and planets form. Conveniently, these Leiden models turned out to be of help in learning about comets and their origins.
"I thought it would be interesting to compare our chemical models with published data on comets," says the astronomer. "Luckily, I had the help of Ewine. We did some statistics to pin down if there was a special time or place in our young solar system, where our chemical models meet the data on comets." This happened to be the case, and to a surprising extent. Where the researchers hoped for a number of comets sharing similarities, it turned out that all fourteen comets showed the same trend. "There was a single model that fitted each comet best, thereby indicating that they share their origin."

Credit: Leiden University[b]Ice-cold[/b]
And that origin is somewhere close to our young Sun, when it was still encircled by a protoplanetary disc and our planets were still forming. The model suggests a zone around the Sun, inside the range where carbon monoxide becomes ice—relatively far away from the nucleus of the young Sun. "At these locations, the temperature varies from 21 to 28 Kelvin, which is around minus 250 degrees Celsius. That's very cold, so cold that almost all the molecules we know are ice.

"From our models, we know that there are some reactions taking place in the ice phase—although very slowly, in a time-frame of 100,000 to 1 million years. But that could explain why there are different comets with different compositions."
But if comets come from the same place, how do they end up in different places and orbits in our solar system? "Although we now think they formed in similar locations around the young Sun, the orbits of some of these comets could be disturbed—for instance by Jupiter—which explains the different orbits."[b]Comet data hunter[/b]
As befits a scientist, Eistrup places some side-notes to his publication. "With only fourteen comets, the sample is quite small. That's why I'm currently hunting for data on many more comets, to run them through our models and further test our hypothesis." Eistrup also hopes that astronomers that study the origin of our solar system and its evolution can use his results. "Our research suggests that comets have formed during the period they're studying, so this new information might give them new insights."
He is also keen to get in touch with other comet researchers. "Because we show a new trend, I would like to discuss what other astronomers think of our research."[b]The seeds of life[/b]
Comets and life on Earth, they go hand in hand. "We still don't know how life on Earth began. But the chemistry on comets could lead to the production of organic molecules, including some building blocks for life. And if the right comet hits the right planet, with the right environment, life could start growing," Eistrup concludes. So, interestingly, understanding the birth of comets potentially could help us understand the birth of life on Earth.